target="external">gunned down and eventually bled to death in the
melee.

"I knew he was going to die," said Friesen, who has had to unearth
the trauma again as the victims, the country -- and the media -- brace
for the 10th anniversary of the most iconic of all
school shootings.

On April 20, 1999, Columbine High School seniors Eric Harris and Dylan Klebold, wielding
automatic weapons, slaughtered 12 students and one teacher. Another
24 were injured in the 45-minute rampage.

Columbine High School Students, Teacher Report Flashbacks

A number of books have tried to dissect the motives of the
killers and the truth behind the event that played out on television
screens across America, but no studies have ever examined the
psychological effects of the massacre on those left behind, according to Dr. Frank Ochberg, a former FBI psychiatrist who guided the
counseling teams in the aftermath of Columbine.

"There were relatively few who were right at the heart of [the
shootings] and were direct post-traumatic stress syndrome candidates,"
Ochberg told ABCNews.com. "But there were relatively many for whom
Columbine was their Gettysburg."

"It changed them, and if they were young, they grew up fast," he said. "Within that group, some are better and some are worse."

Friesen had been holed down in his classroom for three hours that day,
with the incessant blaring of the school alarms, exploding pipe bombs
and students' screams.

"A gun and holster is the worst one for me," said the 58-year-old, who
has retired from teaching and lives in Littleton. "But you live with
it. You learn to cope."

Post-Traumatic Stress Lingers

That takes him back to the frenetic day when Special Weapons and
Tactics, or SWAT, teams, as confused as those already inside the
school, roughed up Friesen, initially believing he was a
suspect.

He said the easiest part of dealing with the shootings was getting free
counseling for his post-traumatic stress disorder, but many never
sought help.

"She saved my life," he said of his counselor. "It was the worst thing I have ever gone through," Friesen told
ABCNews.com. "Post-traumatic stress can happen to anybody. It's
mind-boggling to know that people still don't believe in it. It's
real, and it's one of those things that just won't go away unless you
get help."